Maximum span by grade
| Grade | Maximum span |
|---|---|
| Select Structural | 19′-9″ |
| No. 1 | 16′-1″ |
| No. 2 | 15′-3″ |
| No. 3 | - |
Span tables · Rafters · 30 psf snow
30 psf live · L/180
2x10 Douglas Fir-Larch rafter span at 24″ o.c.
At 24″ o.c., a 2x10 Douglas Fir-Larch #2 rafter spans up to 15′-3″ under this table's load case. Select Structural and No. 1 reach further; No. 3 less. See the full grade breakdown below.
Douglas Fir-Larch #2, 30 psf
What this span means
This is the maximum clear span the Table R802.4.1(3) permits for a 2x10 Douglas Fir-Larch rafter spaced 24″ o.c., carrying 30 psf of live load plus 10 psf dead load with a L/180 deflection limit. Rafter spans are the horizontal projection. A blank cell in the Select Structural, No. 1 or No. 2 rows means the source table gives a note rather than a span for that size. No. 3 rafter spans are published in the source table but are not reproduced here - look them up in the cited table.
Actual allowable spans depend on your real loads, the lumber's moisture and exact grade stamp, bearing and connection details, and any point loads or openings. Treat this as a starting point, then confirm the member with your local code and a design professional.
The figure above is a clear span between the faces of the supports, not the length of the board - how to read a span table covers that and the other misreadings worth checking before you cut. For what the L/180 limit in this table's heading is doing to the number, see what L/360 deflection means; for what the 24″ o.c. spacing costs, 16 in vs 24 in on center.
Source: International Residential Code (IRC), 2018 - Table R802.4.1(3) - Rafter Spans, 30 psf Ground Snow Load (ceiling not attached, L/180). Published by International Code Council.
Edition: These values are transcribed from the IRC 2018 tables. The ICC has since published IRC 2021 and IRC 2024, and the edition in force varies by jurisdiction - confirm the table and edition adopted by your local building department before relying on a span.
Frequently asked questions
How far can a 2x10 Douglas Fir-Larch rafter span at 24″ o.c.?
A No. 2 2x10 Douglas Fir-Larch rafter spaced 24″ o.c. spans up to 15′-3″ under 30 psf live load plus 10 psf dead load, with deflection limited to L/180. That figure is the clear span between the faces of the supports, not the length of the board. Source: International Residential Code (IRC), 2018 - Table R802.4.1(3) - Rafter Spans, 30 psf Ground Snow Load (ceiling not attached, L/180) (International Code Council).
Does the lumber grade change how far a 2x10 Douglas Fir-Larch rafter spans?
The table publishes a separate span per grade. At 24″ o.c., a 2x10 Douglas Fir-Larch rafter spans Select Structural 19′-9″, No. 1 16′-1″ and No. 2 15′-3″. Douglas Fir-Larch is the species group the table was published for and the grade is the stamp on the board, so both have to match the lumber you actually buy. Rafter spans are the horizontal projection. A blank cell in the Select Structural, No. 1 or No. 2 rows means the source table gives a note rather than a span for that size. No. 3 rafter spans are published in the source table but are not reproduced here - look them up in the cited table.
What is the span for a 2x10 Douglas Fir-Larch rafter at other on-center spacings?
The source table publishes a separate span for every on-center spacing, and the span never gets longer as the spacing widens. For a No. 2 2x10 Douglas Fir-Larch rafter under this load case: 12″ o.c. 21′-7″, 16″ o.c. 18′-9″, 19.2″ o.c. 17′-1″ and 24″ o.c. 15′-3″. This page reports the 24″ o.c. row.
What load case does this 2x10 Douglas Fir-Larch rafter span assume?
Rafters - 30 psf Ground Snow Load: 30 psf live load plus 10 psf dead load, with deflection limited to L/180. Sloped roof rafters where the ceiling is not attached to the rafters (30 psf ground snow load). Source: International Residential Code (IRC), 2018 - Table R802.4.1(3) - Rafter Spans, 30 psf Ground Snow Load (ceiling not attached, L/180) (International Code Council).
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